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Freon level

99 lumina. Ac was not working. I added a few oz’s and the compressor clicked on but cooling fans were not running. After 10 min of idling the fans did come on but went off after 1-2 minutes. It seemed like they were responding to coolant temp more than ac pressure. Do the fans run when the hi pressure rises to a certain point where the computer will turn on fans?

The PCM controls the cooling fans based on the input from the refrigerant pressure sensor. You need more pressure for the fans to turn on.

I hooked up hose set but did not open valve and compressor did click on. Which seemed odd. Added about 8oz and vents were cold. I am going to drive car for few days and monitor ac performance.

From your first post I got the impression that the system was empty before you added 2 ounces, perhaps not. Without a sight glass it can be difficult for the DIY person to verify if the system is fully charged. The suction line from the firewall should be cool to cold with the blower on high, if not the system is under charged. Add slowly and recheck in 2 oz. increments.

I am not sure I understand what you mean by hooking up a hose set but not opening the valve. How did you add the 8oz if the valve was not open?

The compressor will come on as long as the pressure in the low and high lines are within an acceptable range (varies from car to car), but that does not mean there is sufficient freon in the system to cool the air.

for the fan to cycle on and off is perfectly normal and is controlled by the pressure sensors. The compressor does the same. You normally don’t feel or realize it when you drive because your attention is on the road and the temperature is maintained during the cycling. However, cycling too frequently can be an indication of low or too high pressure.

ac did not work when it was switched on. I hooked up cheapo recharge hose to suction side butI did not open can valve. Before I could open valve, the compressor clicked on. I than added about 8oz. Vent temp slowly dropped as I added the 8oz. It’s a friends car. It sat for 4 yrs. it has 70k miles. Great shape. They said the ac is working fine today.

If the accumulater drier is sweating the system is operating OK. To safely and properly check and correct system pressure it is necessary to monitor high and low side pressure while safely operating the ac. With all valves closed on the gauge manifold and the AC running with an adequate fan in front of the grill cooling the condensor the low side should be about 30psi and the high side less than 300psi. The high side pressure is highly dependent on ambient temperature and humidity. 300 psi is the upper end of the operating range of most vehicles I recall working on.